Global Navigation Satellite Systems (GNSS) provide geographical positioning information from a plurality of orbiting satellites to receivers around the globe including at sea, on the ground, and in the air. The best known of these systems is the U.S. Global Positioning System (GPS), but other systems, such as the Russian GLONASS system, the European Union's Galileo, and China's Compass systems, provide a similar service. They are collectively known as Global Navigation Satellite Systems, and they can provide position accuracies in the range of about ten (10) meters to about fifteen (15) meters. Although the satellites can potentially provide more accurate positions, atmospheric and other effects degrade the quality of the satellite signals.
Unfortunately, GNSS systems are not sufficiently accurate for all applications. An agricultural vehicle operating in a field, for example, may require positioning accuracies of less than one (1) meter. Satellite signals from GNSS systems can be corrected by using one or more reference stations at precisely known locations, which broadcast corrections to GNSS receivers, by way of geostationary satellites for instance (e.g., via Satellite Based Augmentation Systems), in the vicinity of the reference stations. This technique is known as a Differential GNSS (DGNSS) service and it is used to enable precise navigation for ships, aircrafts, and ground vehicles (e.g., vehicles). Positioning systems that leverage the DGNSS service using reference stations and geostationary satellites have sub-meter level precision, enabling tractors to cross agricultural fields in precisely the same track every time, improving crop yields, and in other industries, enabling snow plows, for instance, to operate quickly over roads buried beneath an otherwise trackless snow field. Some systems can achieve decimeter-level precision, where satellites are used to measure ionosphere and clock errors and then pass the resulting corrections to receivers.
Real Time Kinematic (RTK) satellite navigation is another technique used to enhance the precision of position data derived from satellite-based positioning systems using measurements of the phase(s) of a tracked satellite signal's carrier wave(s), rather than the information content of the signal. RTK systems use a single base station transceiver (or transmitter) as a reference station (e.g., with known geographical coordinates) to provide real-time corrections or correctors to a number of mobile units (e.g., rover receiver units). The base station broadcasts the correction to the observed phase based on its known location, and the mobile units apply the broadcast correction to their own respective phase measurements. The range of an RTK base station is limited, and the RTK base station may use a real-time communications channel, such as an RF signal, to communicate GNSS information (e.g., correction information or correctors) to the mobile units (e.g., vehicles).